So-called “zooming” is known as a display technique for enlarging and reducing the size of any area of an image, which is displayed on a screen, to display the area at an optimum size. Zooming generally can be classified as follows depending upon how what particular area of an image displayed on a screen is zoomed: First, the entire screen is displayed upon zooming it to any size using the center of the screen as a reference. This is the most common type of zooming (for example, see the specification of Japanese Patent Application Laid-Open No. 09-026769). Second, there is zooming referred to as “point zooming”. In this type of zooming, zooming is performed to any size centered on a point that the operator has designated in an image displayed on a screen, and the zoom display is presented in such a manner that the point is situated at the center of the screen after zooming (for example, see the specification of Japanese Patent Application Laid-Open No. 2001-324974). Third, there is zooming referred to as “area zooming”. In this type of zooming, the zoom display is presented in such a manner that the area specified by the operator is zoomed so as to fit the size of the screen (for example, see the specification of Japanese Patent Application Laid-Open No. 11-282454).
Further, methods of designating an area (method of area designation operation) used in the “area zooming” known generally include a method of designating a rectangle based upon a diagonal line and a method of designating the area upon changing the position or size of a rectangle provided in advance.
However, in the first type of zooming (Japanese Patent Application Laid-Open No. 09-026769), the fact that the zooming reference is the center of the screen means that the image zoomed and displayed on the screen will not necessarily coincide with the area that the operator actually desires to be zoomed and displayed. For this reason, the operator must perform a position adjustment appropriately using vertical and horizontal scrolling functions (and carry out zooming again in certain cases) after zooming in such a manner that the area that the operator desires to be zoomed will be displayed upon being fitted to the screen.
In the case of the second type of zooming (Japanese Patent Application Laid-Open No. 2001-324974), the point desired to be zoomed and displayed can be designated by the operator, but since zooming is performed centered on the point designated by the operator, it is required that the operator designate accurately the center position of the area desired to be zoomed and displayed. In actuality, however, it is difficult for the operator to designate the center position accurately, and the zoom display obtained may not coincide with the area the user desires to zoom and display. As in the first type of zooming, it is necessary for the operator to perform a position adjustment appropriately (and carry out zooming again in certain cases) after zooming so as to display the image on the screen as desired.
In the third type of zooming (Japanese Patent Application Laid-Open No. 11-282454), the area desired to be zoomed and displayed can be designated at will and displayed so as to fit the size of the screen. This makes it possible to avoid the problem of non-coincidence between the area desired to be zoomed and displayed and the area actually zoomed and displayed. However, in order to implement area zooming, areas desired to be zoomed and displayed require commands individually, whenever zooming is carried out, through use of designating input means such as a pointing device to enter the extent of the area desired to be zoomed and displayed. When it is desired to perform zooming with respect to a plurality of areas, a technical problem which arises is poor operability.
Furthermore, in instances where part of an image that will not fit on the screen is zoomed, it is required with all of the first to third types of zooming that the image be moved using the vertical and horizontal zooming functions before zooming so that the area desired to be zoomed and displayed will be displayed temporarily on the screen. In this case also a technical problem which arises is poor operability.
Another method of designating an area is to analyze image information, extract an area based upon the layout or features using a recognition technique and designating this area as the scope of the display (see the specifications of Japanese Patent Application Laid-Open Nos. 06-282258 and 08-202856). However, this method not only is not effective for application to an image from which features are difficult to extract, but the user must also perform a selecting and specifying operation with respect to areas that have been decided as a result of automatic recognition. Consequently, a technical problem which arises is poor operability in a case where an area desired to be displayed has been decided beforehand.